This invention relates generally to the field of medical devices, and more particularly to a guide wire for advancing a catheter or other intraluminal device within a body lumen in a procedure such as percutaneous transluminal coronary angioplasty (PTCA) or stent delivery which is observed by Magnetic Resonance Imaging (MRI).
Conventional guide wires for angioplasty and other vascular procedures usually comprise an elongated core member with one or more tapered sections near the distal end thereof and a flexible body such as a helical coil disposed about the distal portion of the core member. A shapeable member, which may be the distal extremity of the core member or a separate shaping ribbon which is secured to the distal extremity of the core member, extends through the flexible body and is secured to a rounded plug at the distal end of the flexible body. Torquing means are provided on the proximal end of the core member to rotate, and thereby steer, the guide wire while it is being advanced through a patient""s vascular system.
In a typical PTCA procedure, a guiding catheter having a preformed distal tip is percutaneously introduced into the cardiovascular system of a patient in a conventional Seldinger technique and advanced therein until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guide wire is positioned within an inner lumen of a dilatation catheter and then both are advanced through the guiding catheter to the distal end thereof. The guide wire is first advanced out of the distal end of the guiding catheter into the patient""s coronary vasculature until the distal end of the guide wire crosses a lesion to be dilated, then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient""s coronary anatomy over the previously introduced guide wire until the balloon of the dilatation catheter is properly positioned across the lesion. Once in position across the lesion, the balloon is inflated to a predetermined size with radiopaque liquid at relatively high pressures (e.g., greater than 4 atmospheres) to press the arteriosclerotic plaque of the lesion against the inside of the artery wall and to otherwise expand the inner lumen of the artery. The balloon is then deflated so that blood flow is resumed through the dilated artery and the dilatation catheter can be removed therefrom.
A major requirement for guide wires is that they have sufficient column strength to be pushed through a patient""s vascular system or other body lumen without kinking. However, they must also be flexible enough to avoid damaging the blood vessel or other body lumen through which they are advanced. Efforts have been made to improve both the strength and flexibility of guide wires to make them more suitable for their intended uses, but these two properties are for the most part diametrically opposed to one another in that an increase in one usually involves a decrease in the other.
Currently, x-ray fluoroscopy is the preferred imaging modality for cardiovascular interventional procedures because no other imaging method has the temporal or spatial resolution provided by fluoroscopy. However, x-ray imaging has many drawbacks for both the patient and the clinician. The iodinated contrast agents employed in x-ray fluoroscopy are nephrotoxic with a low but measurable incidence of short-term renal failure and allergic reactivity. The ionizing radiation from the x-ray fluoroscopy can be an issue for the patient during protracted or repeated interventions and is a daily issue for the interventionalist and staff who must cope with the burden of personal dose monitoring and wearing lead shielding.
The use of MRI for observing interventional procedures has been performed for balloon angioplasty and stent placement. The use of this imaging modality is quite attractive because it eliminates some of the problems inherent with x-ray imaging. On the other hand, conventional guide wires which are suitable for x-ray fluoroscopy are not suitable for use in MRI observed interventional procedures due to their magnetic attraction, large magnetic susceptibility artifact, and potential heating when exposed to RF energy.
What has been needed and heretofore unavailable is a guide wire which is safe and compatible for use in conjunction with MRI. The present invention satisfies these and other needs.
The present invention is directed to an intracorporeal device such as a guide wire which is safe, compatible and readily visible with MRI. An intracorporeal device embodying features of the invention preferably has an elongated member with an electrically non-conductive proximal section, an essentially non-magnetic distal core section, and a metallic coil disposed about and secured to the distal core section with a small magnetic susceptibility to act as an MRI visible marker. That is, the coil or a marker thereon has a magnetic susceptibility that facilitates the observation thereof within the patient under MRI.
The distal end of the proximal non-conductive core section and the proximal end of the non-magnetic but conductive distal core section can be secured together by any non-conductive means including polymeric or metallic sleeves so long as the joint between these members results in a torque transmitting relationship therebetween.
The selection of materials for component parts of the intracorporeal device, such as a guide wire, including the proximal section, the distal section and the MRI visible member secured to the distal section are based upon the mechanical and physical properties needed for the intended use. The materials from which the MRI compatible device is made need to overcome three basic factors: magnetic attraction of magnetic members, RF heating effects of conductive members, and visualization under MRI.
Forming the proximal section from non-conductive, non-metallic material and the distal section and MRI visible member from non-magnetic materials resolves the magnetic attraction of these members during MRI. The non-conductive, non-metallic nature of the proximal core section and the length of the distal core section alone or in conjunction with the MRI visible member resolve the RF heating of these members. Controlling the level of magnetic susceptibility of the material from which the MRI visible member is formed resolves the visualization issue.
Suitable materials for the non-conductive proximal section of the intracorporeal device include optical fibers (single or a bundle of fibers), fiberglass, carbon fiber-epoxy composites, composites of oriented polyethylene fiber (e.g., Spectra(copyright)), composites of polyaramide fiber (e.g., Kelvar(copyright)) and composites of these materials with engineering resins such as polysulfone, polyethersulfone, polyetherimide, vinylester, cyanate ester, phenolic, polyurethane, polyimide and polyetheretherketone. The MRI visible member or marker and preferably also the distal section are formed of suitable non-magnetic materials that may be electrically conductive. Suitable materials include one or more metallic materials selected from the group consisting of platinum, nitinol, niobium, titanium, tantalum, zirconium, iridium, aluminum, silver, gold, indium, and alloys thereof.
The distal core section and the tip coil are formed of suitable non-magnetic conductive materials having the correct amount of magnetic susceptibility artifact for accurate imaging. The volumetric magnetic susceptibility suitable for visualization under MRI for these structures is less than or equal to about 280xc3x9710xe2x88x926 (SI), and preferably less than about 245xc3x9710xe2x88x926 (SI).
The intracorporeal devices embodying features of the present invention are in part readily visible under MRI and they have desirable characteristics for performing intracorporeal procedures. These and other advantages of the invention will become more apparent from the following detailed description thereof when taken in conjunction with the following exemplary drawings.